SAN FRANCISCO - MARCH 5: People rally in front of the California Supreme Court Building after arguments were heard for and against Proposition 8 March 5, 2009 in San Francisco, California. The controversial proposition that prohibits gays and lesbians the right to marry is being challenged by the gay community. (Photo by David Paul Morris/Getty Images)

Photo: David Paul Morris, Getty Images

SAN FRANCISCO - MARCH 5: People rally in front of the California...

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Olena Mikita tries to out shout supporters of same-sex marriages after the California State Supreme Court heard arguments over the constitutionality of Proposition 8.

Photo: Paul Chinn, The Chronicle

Olena Mikita tries to out shout supporters of same-sex marriages...

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The crowd cheers as a speaker calls for victory in the courts at a rally for Marriage Equality in San Francisco on Wednesday, March 4, 2009.

Voters in California are sharply divided on same-sex marriage, and an amendment to overturn Prop. 8 would depend largely on campaigning and voter turnout, according to a Field Poll to be released today.

The California Supreme Court is currently considering challenges to Prop. 8, the initiative passed by voters in November that banned same-sex marriage. Proponents say that if the court doesn't side with them, they will work on a measure to overturn the ban.

Though views on same-sex marriage vary greatly according to age, geography, political party and religious preference, the numbers overall are almost equally split.

"Opinions haven't changed much since November," said Field Poll Director Mark DiCamillo of the election where 52 percent of voters approved Prop. 8. "The closeness of the divide suggests it would depend on the quality of the campaigning and voter turnout."

Voter turnout, according to the poll, could be the deciding factor in an upcoming amendment to allow same-sex couples to marry.

"The success would really depend on who showed up to vote," DiCamillo said.

According to the poll, Democrats favor same-sex marriage by 63 percent and 32 percent oppose. Republicans are 70 percent opposed and 24 percent in favor. In the San Francisco Bay Area, those polled are 64 percent in favor and 31 percent opposed. In Los Angeles County, 55 percent favor and 40 percent oppose.

Voters aged 18 to 39 favor gay marriage by 55 percent while those 65 or older are 58 percent opposed, according to the poll.

Proponents plan to use such polls to decide which voters to target.

"We don't expect the court will rule to overturn Prop. 8 so there will likely be another initiative," said Rick Jacobs, chair and found of the Courage Campaign, an organizing network for progressive causes in California. "The movement understands that we will have to win at the ballot box as soon as it is politically feasible."

Jacobs' group is one of many that are shaping strategies and expanding outreach.

The Courage Campaign is holding events to teach community organizing and campaigning. The first two were in Los Angeles and Fresno.

"We will go county by county to begin in earnest the work of changing hearts and minds," Jacobs said. "We are building our army and the infrastructure to reverse Prop. 8.

"No one did that in the last election."

Those who support the ban on gay marriage are also mobilizing for a future fight.

"No matter what happens with the Supreme Court, this issue will be back and we are starting to get ready for that," said Frank Schubert, a Yes on 8 campaign spokesman. "There is not much doubt that the issue of gay marriage sharply polarizes people. We are in the process of getting our plans and programs together."

Equality California, a nonprofit LGBT advocacy group, is one of the No on 8 groups expanding its focus. On Monday, Andrea Shorter took a leave from her job as director of And Marriage for All, a Northern California coalition opposed to Prop. 8, to take on the role of statewide coalition coordinator for Equality California. In her new post, she will work to strengthen connections between LGBT groups and communities of color and different religious groups.

"There is a lot of interest in terms of another ballot initiative," Shorter said. "The poll may inform us how to mount the best campaign."